Frogs and other amphibians around the world are in the middle of an extinction crisis. A deadly, fast-moving fungus called Batrachochytrium dendrobatidis (Bd) has spread to at least 52 countries since it was first observed in 1993 and has driven as many as 100 species into extinction since.

Scientists still don’t fully understand the Bd fungus, or chytridiomycosis, the deadly skin disease that it causes. But new research provides a clue to why it has spread: According to a paper published last month in Environmental Science & Technology, young frogs exposed to flame retardants end up with a weakened immune system, a condition that researchers theorize may contribute to the high mortality rate the chytrid fungus or other pathogens induce.

“Making antibodies to get rid of pathogens is vital to frogs’ ability to fend off disease,” lead author Tawnya Cary, a postdoctoral scholar at the University of Wisconsin, Madison, told Environmental Health News.

Cary and the research team at the Karasov Lab at UW-Madison have been investigating the effect of fire retardants and other chemicals in the state’s waterways for several years. This 2011 video shows leopard frog tadpoles being exposed to various levels of flame retardants called polybrominated diphenyl ethers (PBDEs) through their diet.

PBDEs—once commonly used in plastics, electronics, furniture cushions, and more—have not been in use in the U.S. for about 10 years. Yet they persist in the environment through wastewater and through leaching out of long-lived products such as furniture. Once there, they can get into in the water or into plants or other foods that animals eat, and from there into humans. PBDE exposure has been linked to decreased female fertility and lower infant birthweight in humans and to weakened immune systems and other health conditions in wildlife.

For this new study, the researchers exposed frog tadpoles to several “environmentally realistic” levels of PBDEs, consistent with what the little wigglers might be exposed to in their natural habitats. One group of tadpoles was exposed to 634 nanograms of PBDEs in every gram of food. When they grew to full size, the frogs produced 66 percent fewer antibodies than a group of frogs that had not been exposed to the chemicals. Two other groups of frogs that were exposed to even smaller amounts of flame retardants—as low as 1.1 nanograms—ended up even worse off. They produced 89 percent and 92 percent fewer antibodies, respectively. That’s not a quirk of the study: It backs up similar results in other tests with other species that experienced more extreme levels of immunodeficiency after exposure to low levels of PBDEs.

Flammability researcher Alexander Morgan of the University of Dayton Research Institute, who was not affiliated with this study, said he wasn’t surprised that the chemical exposure caused a reaction in the frogs but questioned whether the chemicals used in the lab were the same ones frogs might encounter in the wild. “You cannot buy PBDEs anymore in the U.S.,” he said, pointing out that the chemicals for this study were manufactured by an outside lab and that their purity was, as noted in the paper, undetermined. “The uncertainty about the impurity is a bit concerning,” Morgan said. “It could be something very small in the mixture that is the primary culprit.” He also wondered if the rabbit chow that was fed to the frogs could have reacted with the PBDEs in some way. He suspects that PBDEs could still be the cause of the frogs’ high mortality from chytridiomycosis but worries about the unknown factors in the study.

Kerry Kriger, founder of the nonprofit Save the Frogs, who has worked extensively with the chytrid fungus, also said, “It is no surprise that chemicals would have a negative effect on amphibians.” In addition, he expressed concern about the ethics of the experiment. “I think that laboratories should cease using frogs as study subjects when there is high reason to believe the frogs tested will be malformed, unless those researchers plan to follow through with their results and actively advocate for regulations on those chemicals. Otherwise they are merely killing and deforming frogs.” It’s a provocative point, as the question of whether researchers should take policy positions based on their own or others’ work (particularly on climate change) is an issue the scientific community is grappling with.

Flame retardants have been extensively used since the 1970s, when California first passed rules requiring their use. At the time, they were intended to suppress fires from dropped lit cigarettes. The tobacco industry spent millions of dollars pushing against proposed requirements to create so-called “fire-safe” cigarettes, which it claimed would mean a less desirable product, and instead advocated for federal rules for flame-retardant furniture, according to a 2012 investigation by the Chicago Tribune. The retardants instead made many items more flammable, and the chemicals have since been linked to a variety of health conditions. The chemicals from those earliest flame retardants are expected to linger in the environment for generations, according to a recent report from Scientific American. That’s even more bad news for frogs.

About Us

TakePart is the digital news and lifestyle magazine from Participant Media, the company behind such acclaimed documentaries as CITIZENFOUR, An Inconvenient Truth and Food, Inc. and feature films including Lincoln and Spotlight.